DC-DC converter selection

Discussion in 'The Projects Forum' started by evaine23, May 20, 2011.

  1. evaine23

    Thread Starter New Member

    Jun 13, 2010
    I’m trying to find an efficient means of regulating the output from a battery for a few of my projects but I’m not sure which configuration would result in the longest battery life for the lowest cost. I would like to output a steady 2.5v to 3.3v from two AA batteries, one project draws < 10mA and the other is probably in the same ballpark although I haven’t finished it yet. I believe for maximum battery life I would have to go with a switching regulator. As I need a steady 2.5v-3.3v source I would need to have the voltage reduced with a fresh battery and boosted with older batteries. I think I have three options but I don’t know which one is the most efficient. I could use a SEPIC converter and connect the batteries in series, a step-up converter with the batteries connected in parallel, or a step-up/down converter with a built in LDO and the batteries connected in series. I was reading the Maxim application notes and they mentioned that the step-up/LDO combo was actually more efficient than the SEPIC for loads over about 7mA (Step-up Converter with LDO Beats SEPIC Efficiency - Maxim). I was considering using the MAX710/1 which uses the LDO when Vin>Vout and the boost converter when Vin<Vout. I didn’t know if it would kill my battery until Vin < Vout however, and the chips cost around $8 each which is a little more than I would like to spend. The SEPIC just seems a little complicated to me but if it was the best option I would consider it. What I really would like to know is weather a two parallel batteries and a boost converter would be more efficient than two batteries in series with the step-up/LDO combo or if I should attempt a SEPIC converter.